When Christopher Biggs, a Ph.D. student at the University of Texas at Austin, set out to study the breeding habits of spotted seatrout, he didn’t have hurricane research on his mind.

“We’re really interested in looking at where fish spawn, and how they spawn, so we can better understand how productive they are,” Biggs told Eos. The males of this estuarine species make low-pitched croaking sounds when spawning, and Biggs sought to track their spawning behavior using underwater microphones.

But more than 4 months into his 2017 study, the clouds of Hurricane Harvey grew over the Gulf of Mexico. In the course of just a few hours, the storm accelerated from a tropical storm to a category 4 hurricane. And Aransas Bay, where Biggs’s study was taking place, sat dead center in Harvey’s tracks.

Two microphones sat directly under the eye of Harvey for 3 hours, providing the first evidence of fish spawning amid a hurricane.“I was getting pretty nervous,” Biggs said. “This is all the research for my Ph.D. dissertation, so there’s a lot riding on it.”

Biggs and his team raced around by boat retrieving instruments spread throughout the bay before the mandatory evacuation later that day. But he had time to recover only a little under half of them.

Lucky for Biggs, the majority of the microphones survived, and two of them provided a unique data set that has never been caught on record before. Two microphones sat directly under the eye of Harvey for 3 hours, providing the first evidence of fish spawning amid a hurricane. The authors published the results in a paper in Biology Letters earlier this month.

In the Eye of the Storm

The night that Hurricane Harvey hit, a storm surge more than 1.5 meters high drenched the nearby town of Port Aransas, knocking over power lines and causing gas leaks. Winds gusted up to 200 kilometers per hour, unhinging a 200-ton steel trawler and thrashing it around a marina. Roofs ripped off houses, and coastlines choked with debris.

But farther in the bay, the hurricane barely registered to the seatrout.

“That was pretty amazing that they were spawning during the hurricane, right in the middle of the eye of the storm.”The microphone readings during much of the storm are a garble of hurricane whirling, but when the eye passed overhead at around 8:00 p.m. local time, Biggs and his team began to hear the telltale croaking of the trout. Out in the middle of the bay, some dozen or so fish were answering nature’s call.

“That was pretty amazing that they were spawning during the hurricane, right in the middle of the eye of the storm,” Biggs said.

The fish continued spawning until 11:47 p.m. that night, when the storm and its roar overtook the area once again. Biggs said that they can’t be sure whether the fish continued spawning once the eye had passed.

Keep Calm and Spawn On

In the days following the hurricane, as Harvey moved farther on land to deluge Houston, the fish continued to meet for their nightly ritual. For the first 5 days after the storm, however, the fish began spawning 2 hours earlier than usual, a stark change from their behavior before the storm. The scientists believe that colder temperatures may be to blame: Fresh water from the storm cooled the bay’s waters by roughly 5°C and may have confused fish into spawning earlier in the day, as they do in the cooler waters of spring.

“This gives us some idea how fish could respond to increased storm events that are expected to come during climate change.”Biggs says that the results of the latest study are a testament to the fish’s resiliency: His data show that the spotted seatrout spawned every day of the spawning season, despite the Texas coast being bombarded by the largest storm since 1961. And even when the colder temperatures changed the timing of spawning, the effect lasted less than a week after the storm.

“This gives us some idea how fish could respond to increased storm events that are expected to come during climate change,” Biggs explained.

Scientist James Locascio from the Mote Marine Laboratory in Sarasota, Fla., who was not involved in the study, said that it’s important to document how fish survive extreme events. Locascio authored a study from 2005 that recorded fish spawning just hours after Hurricane Charley passed over Florida. He urges future researchers to focus on how human changes at the shoreline could affect fish.

“From a conservation and management perspective, I think it is more important for us to understand the effects of human-induced habitat alterations on these populations,” Locascio said.

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